Summary/Abstract The principal focus of this proposal is to develop polyisoprenylated cysteinyl amide inhibitors (PCAIs) as a novel class of targeted therapies to address the void of effective drugs for the treatment of triple negative breast cancer (TNBC) that afflicts a significantly higher proportion of African Americans. Hyperactivities of polyisoprenylated pathway proteins and their modulating factors are currently the principal drivers of the most difficult-to-treat cancers such as TNBC. In fact, Cdc42 and EGFR/HER1 are overexpressed in 95% and 91% of breast cancers, respectively. RASA1 loss-of-function mutations in 61% and 72% of breast cancers and TNBC, respectively, is functionally equivalent to Ras hyperactivity given its role as a Ras-GTPase. Developing effective drugs for cancers with hyperactivities of Ras and related proteins has been very challenging. Despite numerous efforts, there are no effective therapies for cancers with these aberrations. This proposal adopts a hitherto unexplored approach to address this problem using an entirely novel class of compounds targeting polyisoprenylated protein metabolism and function. This is based on previous studies showing that polyisoprenylation pathway modifications are essential for polyisoprenylated protein control on cell proliferation, differentiation, apoptosis and cytoskeletal organization. The studies will address the hypothesis that PCAIs disrupt signaling pathways that promote cancer cell proliferation and tumor growth as well as the cell migration and invasion that promote metastastic TNBC. This is rationalized by the vast evidence in the scientific literature showing that hyperactivities of monomeric G-proteins drive a large number of TNBC cases and our own preliminary results clearly showing the effectiveness of the PCAIs to block 3D spheroid invasion, apoptosis, angiogenesis and inhibition of TNBC xenograft tumor volume. Furthermore, our other findings reveal that non-cytotoxic concentrations disrupt F-actin organization and lower the levels of key proteins that mediate F-actin organization. The proposed studies are therefore aimed at broadening these studies by (1) Synthesizing new PCAIs analogs and determining their detailed inhibitory effects against basal and EGF- and VEGF-induced 3 D spheroid TNBC cell growth and invasion, (2) Determining the anticancer mechanisms of PCAIs (3) Determining the in vivo effects of the PCAIs in 3D patient- derived TNBC organoids and in TNBC xenografts. It is anticipated that upon the completion of the studies, a clear rationale for the continuous development of this entirely new class of drugs to treat TNBC that disproportionately affects minorities will be firmly established.